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At least 271 records · Page 15Linked to original sources
PubMed1996

Determination of short-chain aliphatic, oxo- and hydroxy-acids in drinking water at low microgram per liter concentrations.

A fast and reliable ion chromatography method has been developed and applied to study the formation and consumption of organic acid ozonation by-products in a drinking water treatment plant. Water samples are injected directly into the ion chromatograph using a large sample loop (740 mu l) without any sample preparation step other than possibly filtration. Organic and inorganic anions are determined by separation on a high-capacity anion-exchange column followed by conductivity detection. The average recovery for the organic acids investigated (beta-hydroxybutyric, acetic, glycolic, butyric, formic, alpha-ketobutyric and pyruvic acid) ranged from 96 to 105%, and their method detection limits ranged from 1 to 5 mu g/l. When applied to samples taken from a drinking water treatment plant, the method proved to be reliable.

3-Hydroxybutyric Acid↗
PubMed1992

In vivo degradation of massive poly(alpha-hydroxy acids): validation of in vitro findings.

The degradation of various high-molecular-weight aliphatic polyesters derived from glycolic acid and/or lactic acid enantiomers was previously investigated in vitro. It was demonstrated that the bulk degradation mechanism proposed in the literature actually proceeds heterogeneously and proceeds faster in the centre than at the surface of large specimens. In order to compare them, similar compression-moulded specimens were implanted intramuscularly in the backs of rabbits, namely PLA50 (poly(DL-lactic acid)), PLA37.5GA25 (75% DL-lactide and 25% glycolide in the feed) and PLA75GA25 (75% L-lactide and 25% glycolide). These three intrinsically amorphous compounds exhibited faster central degradation. Furthermore, preferential degradation of glycolic acid units and induced crystallization of L-lactic acid enriched fragments were observed in the case of PLA75GA25. These findings are comparable to phenomena observed in vitro and are conclusively supported by the re-examination of some old in vivo results. Accordingly, data reported in this paper validate both the in vitro modelling and new understanding of the degradation of lactic acid/glycolic acid-based aliphatic polyesters reported previously.

Animals↗
PubMed1994

Purification and partial structural and kinetic characterization of an aromatic L-alpha-hydroxy acid dehydrogenase from epimastigotes of Trypanosoma cruzi.

An aromatic L-alpha-hydroxyacid dehydrogenase (AHADH) was purified to homogeneity from epimastigotes of Trypanosoma cruzi by a method involving chromatography on DEAE-cellulose, hydrophobic interaction chromatography on Phenyl-Sepharose and affinity chromatography on Affi-Gel Blue. The purified enzyme showed a single band in SDS-PAGE, with an apparent molecular mass of 36 kDa. Since the apparent molecular mass of the native enzyme, determined by gel filtration, is about 80 kDa, the native enzyme is a dimer of similar subunits. The amino acid composition was determined, as well as the sequences of 4 internal peptides obtained by CNBr cleavage at Met residues, and one peptide obtained after tryptic digestion. Three of the peptides presented considerable sequence similarity with the corresponding sequences of several malate dehydrogenases. The optimal pH for the enzyme reaction with p-hydroxyphenyl pyruvate and NADH as substrates was 7.5; that for the reverse reaction was 9.5. The apparent Km values for phenylpyruvate and p-hydroxyphenyl-pyruvate were 48 and 117 microM, respectively; that for L-phenyllactate in the reverse reaction was 420 microM. The enzyme was much less active with alpha-isocaproic acid as substrate, and other acids, including pyruvic and oxaloacetic, were not substrates at all. L-phenyllactic acid, but not the D-isomer, acted as substrate. The enzyme can therefore be considered as a general aromatic L-alpha-hydroxyacid dehydrogenase. The low apparent Km value for NADH (25 microM in the presence of phenylpyruvate) makes AHADH a candidate for the reoxidation of cytosolic NADH in T. cruzi.

Alcohol Oxidoreductases↗
PubMed2006

Enantioselective scandium-catalyzed vinylsilane additions: a new approach to the synthesis of enantiopure beta,gamma-unsaturated alpha-hydroxy acid derivatives.

The development of the Lewis acid-catalyzed alkenylation using trimethylvinylsilanes is described. Both aliphatic and aromatic vinylsilanes were effective nucleophiles at room temperature affording chiral allylic alcohol products in excellent enantioselectivities (97 --> 99% ee) and in moderate to good yields (45-99%). Complete retention of vinysilane geometry was observed where applicable.

Acids↗